Thermostat metal and method of making

ABSTRACT

An improved composite edgelay bimetal material useful as a thermostat metal is shown to have two relatively wide and thin strips of metal of different coefficients of thermal expansion interfacially bonded together along corresponding thin lateral edges of the respective strips, the interfacial bond being a metallurgical bond which is substantially complete along the strip edges. The bond formed between the edges of the metal strips does not significantly alter the properties of the strip materials adjacent the bond and therefore avoids a thermostatically inactive portion of the composite material at the location of the interfacial bond. The improved composite edgelay material is formed by disposing two metal rods of hexagonal cross-sectional configuration or the like so that narrow surfaces of the rods are engaged along the length of the rods. The rods are resistance welded together along said engaged surfaces and, preferably after treatment for improvement of the weld bond between the rods, the rods are deformed in a rolling mill or the like to reduce the rods into respective wide and thin metal strips which are secured together along thin lateral edges of the strips by said bond.

United States Patent wu iv [11] 3,811,028

Henry et al. 7 May 14, 1974 THERMOSTAT METAL AND METHOD OF [57] ABSTRACTI MAKING An improved composite edgelay bimetal material use- [75]Inventors: Ty Henry; Rene A. Dubuc, both of ful as a thermostat metal isshown to have two rela- Attleboro, Mass. tively wide and thin strips ofmetal of different coefficients of thermal expansion interfaciallybonded to- [73] I Assignee: Texas Instruments Incorporated gether alongcorresponding thin lateral edges of the Dallas I respective strips, theinterfacial bond being a metallur- [22] Filed: June 24, 1969 gical bondwhichis substantially complete along the strip edges. The bond formedbetween the ed es of [2]] Appl' the metal strips does not significantlyalter the p operties of the strip materials adjacent the bond and there-[52] US. Cl, 219/117 R, 219/833, 29/480, fore avoids a thermostaticallyinactive portion of the a 29/4975 composite material at the location ofthe interfacial [51] Int. Cl B23k 11/06 nd. The improved compositeedgelay material is [58] Field of Search.....'. 219/82, 83, 117 R;29/480, forme by isposing two metal rods of hexagonal I 29/4975, 498cross-sectional configuration or the like so that narrow surfaces of therods are engaged along the length of [56] References Cited the rods. Therods are resistance welded together UNITED STATES PATENTS along saidengaged surfaces and, preferably afte. treatment for improvement of theweld bond between Z: 3111111111315 ",24: the rods, the rods are deformedin a rolling mill or the 219/1 R like to reduce the rods into respectivewide and thin 2|9/1 17 R metal strips which are secured together alongthin lat- 2l9/1 17 R x eral edges of the strips by said bond.

3,095,500 6/1963 Jost 3,092,715 6/1963 Hallas 2,4l4,5ll 1/1947 DyarPrimary Examiner-J. V. Truhe Assistant Examiner-G. 'R.Peterson Attorney,Agent,-0r Firm-Harold Levine; John A. Haug; James P. Mc'Andrews i W lilaims, 9 Drawing Figures ill I I I lllll.

Hill

SHEET 1 [1F 2 PATENTEHMAY-I 4 2974 Inven tons:

ROLL CUT Henry eneA,Du5uc, 2 Atty.

WELD SINTER ROLL ANA/EAL CLEAN THERMOSTAT METAL AND METHOD OF MAKING Atthe present time, composite edgelay bimetals used as thermostat metalsembody relatively wide and thin metal strips of different coefficientsof thermal expansion. These metal strips are secured together along thinedges of the strips. However, these composite materials are commonlymade by means of an inert gas shielded arc weld or the like formedbetween the edges of the metal strips. As a result, the compositematerials have an undesirably wide, porous, and thermostaticallyinactive weld stripe extending centrally along the length of thecomposite material. The porous quality of the weld weakens the bondbetween the metal strips and the presence of the wide weld stripereduces the thermostatic activity or flexivity of the compositematerial. When such composite materials are annealed and reduced inthickness by rolling or the like to introduce a controlled-degree ofwork-hardening into the composite material, as is frequently required,the undesirable weld stripe is further weakened and widened, therebyfurther reducing the reliability and thermostatic activity of thecomposite material. Frequently, when narrow thermostat metal. parts areformed from such composite materials, the thermostatically inactiveportion of the, composite material at the location of .the weld stripewill. comprise a significant portion of the part width with the resultthat the part is able to display only limited thermostatic activity.

In another conventional process for making such composite edgelaybimetals, relatively thick bars of metal are pressure welded together ina rolling mill or the like. The bonded bars are then cut or sliced in adirection lengthwise of the bars and transversely of the plane of thepressure weld to form thin elements which each embody two relativelywide and thin strips of metal bonded together along thin edges of thestrips. In this process, substantial rerolling of the thin elements isusually required, and the bonds which remain after such rolling arefrequently incomplete or of poor quality. The process is also expensiveto perform and wastes a substantial amount of the original bar materialduring the cutting or slicing of the thin elements from the ini tiallybonded metal bars.

It is an object of this invention to provide a novel and improvedcomposite-edgelay bimetal material having two relativelywide and thinstrips of metal bonded together alon'gthin lateral edges of the metalstrips; to

provide such a composite material which is particularly useful as athermostat metal; to provide such a composite edgelay bimetal which issubstantially free of a thermostatically inactive portion at thelocation of the bond between the metal strips embodied in the'compositematerial; to provide such a composite edgelay material in which theinterfacial bond formed between lateral edges of the metal stripsembodied therein is a substantially complete metallurgical bond and isfree of pores; to provide a novel and improved method for makingsuchcomposite edgelay bimetal material; to provide such a methodwhichachieves a strong and complete metallurgical bond between the metalstrips embodied in the composite material; to provide such a methodwhich avoids formation of an undesirably wide weld stripe in thecomposite material; and to provide such a method which is easily andeconomically performed by use of equipment generally available tothermostat metal manufacturers.

Briefly described, the novel and improved method of this inventionincludes the steps of disposing two metal rods of round, hexagonal orother suitable crosssectional configuration so that long and narrowsurfaces of the rods extending along the lengths of the rods are engagedwith each other and so that other long and narrow surfaces of the rodsof relatively greater surface area are disposed to be contacted byelectrical resistance welding electrodes for resistance welding the rodstogether. For example, in a preferred embodiment of this invention, rodsof hexagonal cross-sectional configuration are continuously advancedbetween the resistance welding rolls of conventional seam weldingapparatus so that corresponding flat surfaces of the rods extendingalong the lengths of the rods are continuously brought into engagementwith each other between the welding rolls and so that two or more flatsurfaces of each rod are continuously brought into contact with therespective welding roll surfaces, thereby to grip or press the rodstogether between the rolls while directing electrical current throughthe rods for resis-- tance welding the engaged rod surfaces together.Preferably, the welded rods are then heated to an elevated temperaturefor a suitable period of time for sintering the weld or bond between therods, thereby to complete the bond between the engaged rod surfaces bydiffusion between the rod materials. Particularly where the rodmaterials include iron or iron alloys, the sintering temperature towhich the rods are subjected is sufficiently high to dissolve all oxidesfrom the engaged rod surfaces into the rod materials so that completediffusion bonding can occur, thereby to completely bond the engaged rodsurfaces together. I

In accordance with this invention, the rod materials are then deformedinto respective flat and thin, strip configurations to form a compositeedgelay bimetal material in which the strips formed by the roddeformation are bonded or welded together along thin lateral edges ofthe strips by means of the resistance weld or bond described above. Forexample, in a preferred embodiment of this invention, the welded rods,after treatment for bond improvement, are advanced between a pair ofrolls of a conventional rolling mill so that both rods contact each millroll, the rods then being squeezed between the rolls to deform the rodsinto the -described'strip configurations. In this way, each of the theinvention, the detailed description referring to the drawings in which:

FIG. I is a front elevation view illustrating a thermo stat metal partembodying a composite edgelay bimetal material;

FIG. 2 is a section view along line 2-2 of FIG. 1;

FIG. 3 is a partial diagrammatic view illustrating a step in the novelmethod of this invention;

FIG. 4 is a partial diagrammatic view illustrating'a subsequent step inthe method of FIG. 3;

FIG. 5 is a partial section view to enlarged scale along line 55 of FIG.3;

FIG. 6 is a partial section view to enlarged scale along line 66 of FIG.4;

FIGS. 7 and 8 are section views similar to FIG. 5 illustrating steps inalternate embodiments of the method of this invention; and

FIG. 9 is a block diagram illustrating the sequence of steps in themethod of this invention.

Referring to the drawings, 10 in FIGS. 1 and 2 indicates a thermostatmetal part made from a composite edgelay bimetal material 12 whichembodies a relatively wide and thin strip 14 of a first metal ofrelatively low coefficient'of thermal expansion and a relatively wideand thin strip 16 of another metal of relatively high coefficient ofthermal expansion. These metal strips are interfacially bonded togetherat 18 along corresponding thin lateral edges of the strips; In a typicalpart, the dimensions a, b, c and d may be 0.63, 0.25, 2.00, and 0.06inches respectively. As will be understood, if such a thermostat metalpart provided with apertures 20 and 22 is subjected to an increase intemperature while the portion of the part adjacent the aperture 20 isfixed in place, the differences in thermal expansion in the metal strips14 and 16 will cause the part to flex or move to the position indicatedby the dotted lines 24 in FIG. 1, this motion of the part being usefulin temperature sensing devices and the like. This flexing movementsubjects the interfacial bond 18 toconsiderable stress'so that a highquality of bond is desirable. In addition, if the metal strips 14 and 16are joined together by inertgas shielded arc welding or the like alongthe bond line 18, the bond line or weld stripe extending along thelength of the part will have a substantial width e equal toapproximately the thickness d of the compositematerial. This weld stripeportion of I the composite material will tend to be thermostaticallyinactive and, particularly where the part is long and narrow so that theweld stripe occupies a substantial portion of the part width, will tendto significantly reduce the thermostatic activity or flexivity of thepart 10. It is therefore desirable to maintain a very narrow bond stripewhile achieving a high quality of bond at the location of the stripe.

In accordance with this invention, these objectives are economicallyachieved by forming the composite edgelay bimetal material in the mannerillustrated in. FIGS. 3-9. That is, in accordance with this invention,an elongated metal rod 26 having a hexagonal crosssectionalconfiguration or the like as shown in FIGS. 3 and 5is advanced from asupply reel (not shown) so that a narrow, flat surface portion or stripe26.] extending along the length of the rod is engaged with acorresponding narrow, flat surface 28.1 of another elongated metal rod28 being advanced from its respective supply reel (not shown)Preferably, as illustrated in FIGS. 3 and 5, the rods are engaged in thedescribed manner by advancing the rods between a pair of weldingelectrode rolls 30in a conventional electrical resistance weldingapparatus. As will be understood, the rod 26 is formed of a metal ofrelatively low coefficient of thermal expansion while the rod 28embodies a metal of relatively high coefficient of thermal expansion. Inthis arrangement, the cross-sectional configuration of the rods isselected so that, while relatively long and narrow surfaces 26.] and28.1 extending along the lengths of the rods are engaged with eachother, substantially greater surface areas of the respective rods aredisposed to be contacted by the welding rolls 30. Preferably the weldingrolls are provided with selected groove configurations to facilitatemaking of electrical contact between welding roll surfaces andsubstantial surface areas of the rods. For example, where hexagonal rodsare used as shown in FIG. 5, narrow rod surfaces 26.1 and 28.1 aredisposed to be engaged with each other while surfaces 26.2, 26.3 and26.4 and surfaces 28.2, 28.3 and 28.4 of the respective rods aredisposed to be contacted by the welding rolls, the rolls having taperedgroove surfaces 30.] and 30.2 for contacting surfaces 26.2 and 26.4 ofthe rod 26 and surfaces 28.2 and 28.4 of the rod 28. In thisarrangement, the metal rods 26 and 28 are gripped or squeezed togetherbetween the rolls 30 as the rods are brought into engagement with eachother while, at the same time, electrical current is directed betweenthe rolls through the rods 26 and 28. The large area of contact betweenthe rolls and rods avoids significant heating of the rollrod interfacesto avoid sticking of the rods to the welding rolls while theconcentration of electrical current at the narrow interface between therods themselves rapidly heats the rods at the surfaces 26.1 and 28.1 forresistance welding the rods together as indicated at 32 in FIG. 5. Wherethe metal rods are hexagonal as illustrated in FIG. 5, guiding of therods into engagement with each other is easily accomplished and controlof the surface areas of the rods contacted with each other and with thewelding rolls is easily maintained.

As will be understood, in resistance welding the rods 26 and 28, theweld or metallurgical bond formed between the rod surfaces 26.1 and 28.1preferably extends throughout these rod surfaces in order to achieve ahigh quality of bond between the rods. However, as formation of such acomplete metallurgical bond frequently cannot be assured by thedescribed resistance welding step above, the welded rods are preferablysubjected to a suitable heat treatment or sintering step for assuringcomplete bonding of the rod surfaces 26.1 and 28.1 according to thisinvention. For example, the rods are preferably heated to a temperatureabove the recrystallization temperature of at least one of the rodmaterials and below the melting temperatures of the rod materials topermit completion of the weld or bond between the rod surfaces 26.] and28.1 by conventional diffusion bonding between the rod materials. Whereone or more of the rods resistance welded together is formed of iron oran iron alloy or of another material in which metal oxides formed on therod surfaces 26.1 and 28.1 would tend to inhibit diffusion bonding ofthe surfaces it is found that the rod materials are adapted to dissolvetheir own oxides within the rod materials at temperatures in the rangefrom 0.5 to 0.7 of the absolute melting temperatures of the rodmaterials (as expressed in degrees Kelvin). Therefore, in thesecircumstances, the resistance welded rods are preferably heated to atemperature in the range from 0.5 to 0.7 of the absolute meltingtemperature of the lowest melting rod material, thereby to permitdissolution of oxides from the rod surfaces 26.1 and 28.1 and to permitcomplete diffusion bonding of these rod surfaces to one another.

In accordance with this invention, the welded rods 26 and 28 are thendeformed by roll squeezing or the like for deforming each of the rodsinto a thin strip configuration in such a way that lateral edges of thethin strips formed by the rods are joined together by the resistanceweld'above described. For example, as illustrated in FIGS. 4 and 6, thewelded rods 26 and 28 which had been contacted individually by therespective welding rolls 30 are passed between the rolls 34 of aconventional roll squeezing mill or the like so that each of the rods 26and 28 contacts each of the rolls 34, whereby the rods are reduced inthickness to form each of the rods into a thin strip-likecross-sectional configuration. Dotted lines 26 and 28' in FIG. 6indicate the configuration of the welded rods as advanced between thesqueezing rolls 34. In this regard, it is noted that when rod materialsare advanced through a rolling mill in this manner, the width of therods is not substantially increased, the deformation of rods previouslyresulting in elongation of the rods to form an improved compositeedgelay bimetal material 36 as illustrated in FIG. 6. ln

' this way, it is found that the rods are readily deformed into thinstrips having'a thickness substantially smaller than the width of therod faces 26.1 and 28.1 without any significant reduction in the qualityof the bond formed between the individual strips. The composite edgelaybimetal material 36 is thus found to be of very high quality in that thestrip materials embodied therein are well-bonded together and in thatthe bond stripe (indicated at 32 in FIG. 6) has no significantthickness, thereby avoiding any thermostatically inactive portion of thecomposite material 36 at the location of the bond stripe. In fact, wherethe composite material embodies welded thin-strip configuration each ofwhich has a width to thickness ratio as great as 421, the bond stripewidth in the plane of the width'dimension of said stripe can equal aslittle as 1/10 or less of the thickness of the strip materials as formedby the method of this invention.

For example, in preparing a composite edgelay bimetal material 36embodying Alloy B as the material of relatively low coefficient ofthermal expansion and Alloy as the material of relatively highcoefficient of thermal expansion (see Table l below for the composi tionof Alloy B and Alloy l0), hexagonal rods 26 and 28 each measuring 0.375inches between flat surfaces of the rods are advanced at a rate of 18inches per minute into engagement with each other between the weldingrolls 30 of a conventional seam welding apparatus.

.The rods are used as received from the manufacturer or are cleaned in aconventional pickling bath and fiber brush scrubbing line inconventional manner for removal of oils and other gross contaminants.The rods are subjected to a compressive force of approximately 450pounds per square inch in the seam welder while a current or 450 amperes(220 volts) is directed between the welding rolls 30, thereby toresistance weld the rod surfaces 26.1 and 28.] together. As theseparticular rod materials comprise iron alloys (each of the alloysembodies more than percent iron by weight), the welded rods are thensubjected to sintering in a conventional bell annealing apparatus for aperiod of about 10 to 30 minutes at a temperature in the range fromabout 2,050 to 2,l50 F. Preferably, for example, the welded rods aresintered at a temperature of 2,l00 F. for about 15 minutes, thereby todissolve all oxides from the rod surfaces 26.] and 28.1 into the rodmaterials and to permit complete diffusion bonding of the rod surfaces26.1 and 28.1 to each other. Preferably, for avoiding excessivediscoloration of the rod surfaces, the rods are sintered in a neutral orreducing atmosphere of nitrogen, hydrogen, or cracked city gas or thelike. In accordance with this invention, the welded and sintered rodsare then passed through a conventional rolling mill in the manner abovedescribed wherein the rods are subjected to from 30' to percentreduction in thickness to form the individual rods into respective thinstrip configurations. Desirably, for example, the rods are deformed intorespective strips of approximately 0.375 inches in width having athickness of about 0.115 inches and having corresponding thin lateraledges of the strips bonded together. In this way, the rods 26 and 28 areformed into the composite edgelay bimetal material 36 having theadvantages previously described.

It should also be understood, that composite edgelay bimetal materials36 can embody any selected metal materials within the scope of thisinvention. For example, any of the iron or iron alloy materials setforth in Table l below can be utilized according to the method of thisinvention, provided, of course, that the materials selected from thetable-display a suitable difference in coefficient of thermal expansionto provide the resulting composite bimetal material with the desiredflexivity. As will be understood, the materials set forth in Table l areadapted to dissolve their own oxides therein when sintered for asuitable period of time at a temperature in the range from 0.5 to 0.7 ofthe absolute melting temperatures of the materials as expressed indegrees Kelvin.

TABLE I Manga- Alumnese inum Molybdenum Cobalt Carbon NOTE.-Inaccordance with conventional procedure, the alloys set forth in thistable may also include small quantities of additional constituentspresent as impurities 1n the alloys.

Alternately other materials as set forth in Table ll are also embodiedin the composite edgelay material 36 within the scope ofthis invention.

TABLE II Manganose In addition, copper, tungsten, various stainlesssteels, and other metals are also embodied in the composite material 36within the scope of this invention.

It should be understood that the method of this invention is not limitedto the use of hexagonal rods 26 and 28. For example, as illustrated inFIG. 7, round rods 36 and 38 can be advanced between pressure weldingrolls 40 so that narrow surface stripes of the rods are resistancewelded together as indicated at 42 in FIG. 7, the welding rolls 40preferably being provided with rounded or tapered grooves 40.1 as shownto provide substantial areas of contact between the respective weldingrolls and the round rods 36 and 38. Alternately, as shown in FIG; 8,six-sided rods 44 and 46 having respective relatively narrow surfaces44.1 and, 46.1 to be engaged with each other and having respectiverelatively wide surfaces 44.2 and 46.2 to engage flat welding rolls 48are utilized, these rods being resistance welded together in the mannerdescribed as indicated at 50 in FIG. 8.

It should also be understood that although the composite material 36 isdesirably formed in the manner above described, it is frequentlydesirable to incorporate a controlled degree of work-hardening in thecomposite material prior to use of the composite material then rolled toa further reduced thickness. Preferably for example, this material isannealed at a temperature of l,550 F. for about minutes and is thenrolled again to reduce the material thickness from about 0.1 15 to about0.045 inches. Most desirably, the composite material is cleaned aftersaid annealing and prior to said additional rolling by passing theannealed material through a conventional pickling bath and fiber brushscrubbing line for removal of any scale formed during annealing. Ifdesired, the steps of annealing, cleaning and rolling as indicated at 52in FIG. 9 are repeated several times to achieve the desired gauge priorto cutting of the composite material to form thermostat metal parts suchas those illustrated in FlGS. 1 and 2.

it should be understood that although particular embodiments of thisinvention have been described by way of illustration, this inventionincludes all modifications and equivalents of the described embodimentswhich fall within the scope of the appended claims.

We claim:

1. A method for making a composite edgelay bimetal material having apair of relatively wide and thin elongated metal strips each having athin lateral edge surface joined throughout said edge surface to acorresponding thin lateral edge surface of the other of said strips,said method comprising the steps of forming a metallurgical bond betweena relatively long and narrow surface extending along the length of afirst metal rod and a corresponding, relatively long and narrow surfaceextending along the length of a second metal rod, and simultaneouslysqueezing each of said rods alongside said bond to simultaneouslyelongate each of said rods and to reduce the cross-sectional area ofeach of said rods for deforming the metal rods into respective,relatively wide and thin, elongated metal strips each having a thinlateral edge surface interfacially joined throughout said edge surfaceto a corresponding thin lateral edge surface of the other of said stripsby means of said bond.

2. A method for making a composite edgelay thermostat bimetal materialhaving a. pair of relatively wide and thin elongated metal strips eachhaving a thin lateral edge surface joined throughout said edge surfaceto a corresponding thin lateral edge surface of the other of saidstrips, said method comprising the steps of disposing a first rod ofmetal of relatively low coefficient of thermal expansion and a secondrod of metal of relatively high coefficient of thermal expansion inengagement with each other along long and relatively narrow surfaces ofthe rods which extend along the lengths of the rods, forming anelectrical resistance weld between s aid rgd along said engaged rodsurfaces, and simultaneously squeezing each of said rods alongside saidbond to simultaneously elongate each of said rods and to reduce thecross-sectional area of each of said rods for deforming the metal rodsinto respective, relatively wide and thin, elongated metal strips eachhaving a thin lateral edge interfacially bonded to a corresponding thinlateral edge of the other of said strips by means of s aid weld.

3. A method as set forth in claim 2 wherein saidwelded rods are heatedfor improving the weld between said rods prior to deforming of saidrods.

4. A method for making a composite edgelay thermostat bimetal materialhaving a pair of relatively wide and thin elongated metal strips eachhaving a thin lateral edge surface joined throughout said edge surfaceto a corresponding thin lateral edge surface of the other of saidstrips, said method comprising the steps of advancing a rod of a firstmetal of relatively low coefficient of thermal expansion and another rodof a second metal of relatively high coefficient of thermal expansionbetween a pair of resistance welding electrodes for engaging the rodswith each other along long and narrow surfaces of the rods which extendalong the lengths of the rods and for engaging relatively greatersurface areas of the rods with respective welding electrodes,

directing electrical current between said electrodes through said rodsto form an electrical resistance weld bond between said rods along saidengaged rod surfaces, heating said rods to increase said bond betweensaid engaged rod surfaces by inducing diffusion bonding between the rodmaterials, advancing said rods between a pair of rolls so that each rodengages each of said rolls and simultaneously squeezing each of saidcross-sectional area of each of said rods for deforming said rods intorespective, relatively wide and thin, elongated metal strips'each havinga thin lateral edge interfacially joined to a corresponding thin lateraledge of the other of said metal strips by means of said bond.

5. A method as set forth in claim 4 wherein said rods are initially ofhexagonal cross-sectional configuration and wherein said rods areadvanced between said welding electrodes to engage respective flatsurfaces of said rods with each other along the lengths of said rods.

6. A method as set forth in claim 4 wherein said rods are initially ofround cross-sectional configuration and wherein said rods are advancedbetween said welding electrodes to engage long and narrow surfaces ofsaid rods with each other along the lengths of said rods.

7. A method as set forth in claim 4 wherein said rods are initially ofsix-sided cross-sectional configuration each having a pair of parallelrod surfaces including a relatively long and narrow rod surfaceextending along the length of the rod and a relatively long and widerrod surface extending along the length of the rod, and

rods.

2. A method for making a composite edgelay thermostat bimetal materialhaving a pair of relatively wide and thin elongated metal strips eachhaving a thin lateral edge surface joined throughout said edge surfaceto a corresponding thin lateral edge surface of the other of saidstrips, said method comprising the steps of disposing a first rod ofmetal of relatively low coefficient of thermal expansion and a secondrod of metal of relatively high coefficient of thermal expansion inengagement with each other along long and relatively narrow surfaces ofthe rods which extend along the lengths of the rods, forming anelectrical resistance weld between said rods along said engaged rodsurfaces, and simultaneously squeezing each of said rods alongside saidbond to simultaneously elongate each of said rods and to reduce thecross-sectional area of each of said rods for deforming the metal rodsinto respective, relatively wide and thin, elongated metal strips eachhaving a thin lateral edge interfacially bonded to a corresponding thinlateral edge of the other of said strips by means of said weld.
 3. Amethod as set forth in claim 2 wherein said welded rods are heated forimproving the weld between said rods prior to deforming of said rods. 4.A method for making a composite edgelay thermostat bimetal materialhaving a pair of relatively wide and thin elongated metal strips eachhaving a thin lateral edge surface joined throughout said edge surfaceto a corresponding thin lateral edge surface of the other of saidstrips, said method comprising the steps of advancing a rod of a firstmetal of relatively low coefficient of thermal expansion and another rodof a second metal of relatively high coefficient of thermal expansionbetween a pair of resistance welding electrodes for engaging the rodswith each other along long and narrow surfaces of the rods which extendalong the lengths of the rods and for engaging relatively greatersurface areas of the rods with respective welding electrodes, directingelectrical current between said electrodes through said rods to form anelectrical resistance weld bond between said rods along said engaged rodsurfaces, heating said rods to increase said bond between said engagedrod surfaces by inducing diffusion bonding between the rod materials,advancing said rods between a pair of rolls so that each rod engageseach of said rolls and simultaneously squeezing each of said rodsbetween said rolls alongside said bond to simultaneously elongate eachof said rods and to reduce the cross-sectional area of each of said rodsfor deforming said rods into respective, relatively wide and thin,elongated metal strips each having a thin lateral edge interfaciallyjoined to a corresponding thin lateral edge of the other of said metalstrips by means of said bond.
 5. A method as set forth in claim 4wherein said rods are initially of hexagonal cross-sectionalconfiguration and wherein said rods are advanced between said weldingelectrodes to engage respective flat surfaces of said rods with eachother along the lengths of said rods.
 6. A method as set forth in claim4 wherein said rods are initially of round cross-sectional configurationand wherein said rods are advanced between said welding electrodes toengage long and narrow surfaces of said rods with each other along thelengths of said rods.
 7. A method as set forth in claim 4 wherein saidrods are initially of six-sided cross-sectional configuration eachhaving a pair of parallel rod surfaces including a relatively long andnarrow rod surface extending along the length of the rod and arelatively long and wider rod surface extending along the length of therod, and wherein said rods are advanced between said welding electrodesto engage said narrow rod surfaces with each other and to engage saidwider rod surfaces with said respective welding electrodes.
 8. A methodas set forth in claim 4 wherein rods are squeezed sufficiently fornarrowing said bond between rods.